Introduction In the past, photography has been a process that captured an image on light-sensitive materials. Light rays reflected from the subject passed through a lens and struck film. A latent image was formed in the emulsion, which was made permanent by processing the film. This resulted in a negative that was used to create a positive print. Today’s photographers have secondary choice – digital image capture, or better known as digital photography.
The similarities between conventional and digital image capture end with the light reaching the camera’s film plane. In a traditionally camera, the light causes a latent image to form on the film. With a digital camera, the light rays strike millions of tiny sensors. These sensors can be one of two types:
CCD’s – Charged-Coupled Devices – the most common and wildly used.
CMOS – Complementary Metal Oxide Semiconductors.
Sensors are typically arranged in rows to form a grid or area array. Each sensor is known as a pixel (abbreviation for the term picture element). Cameras are classified by the number of pixels in their array. The higher the pixel rating of a camera, the better the resolution of that camera.
The Basics In place of traditional film, digital cameras use an image sensor (which form the array) to capture images once they pass through the lens. When light strikes the array, a tiny electronic signal is generated by each pixel; the signals intensity will vary depending upon the brightness of the light. The signal intensity is translated by the camera’s programming into shades or levels of gray. Color information is recorded by filtering the light striking the array to obtain three different grayscale channels, one for red, one for blue, and one for green. When the image is reproduced on the computer screen or sent to the printer, software translates the various levels of gray in each channel back into color information for display.
Aperture and Shutter Speed The way that film cameras control the exposure of an image is by varying the amount (aperture) and the time (shutter speed) that the light falls on the film. On many digital cameras, the exposure is controlled by the length of time that the sensors are activated for receiving light. Although this differs from the method employed by film cameras, the exposure settings on digital cameras are expressed in f-stop numbers for aperture and divisions of a second for shutter speeds. These are the equivalent values and this is to ensure uniformity between the two mediums. The means that even though the technology is different, the digital values are given in equivalent film camera terms. Settings are usually set automatically by the camera unless you change the exposure setting.
Camera Resolution The camera resolution is the number of pixels that a camera is capable of capturing on the image array. Many cameras allow you to choose a resolution setting. The higher the overall pixel count a camera has, the greater its resolution.
Memory Memory storage for digital cameras comes in two main types:
On-board memory – much like a hard drive on a computer. (only a few images can be saved)
Removable memory – comes in many forms and sizes. (Sandisk)
LCD Panel Many digital cameras have a LCD panel. It allows you to preview you pictures.
Lenses Most digital cameras now come with a zoom lens. This enables you to vary the focal length from 18-55mm. This allows you to view subjects at a magnified level without having to move too close to them. In some instances, the zoom lens function will sacrifice the picture quality a little, but it can be a useful option to have.